Polymers containing conjugated diene and vinyl aromatic groups, such as tri-block or penta-block copolymer of styrene-butadiene or styrene-isoprene, have already been commercialized in many applications; for example, the polymers have been used as adhesives, soles, and polymer improvers. However, the conjugated diene group and vinyl aromatic group are prone to cracking due to heat or oxidation, exposure to ultra-violet light, or other unfavorable environment, and thus become unstable.
Substantially saturating the polymers by hydrogenation may improve the stability of the polymers, which are broadly used in flexible materials, biomedical material, etc. There are many patents involved in this technology, such as U.S. Pat. No. 5,352,744 which discloses a completely hydrogenated polymer having a saturation degree higher than 99.5% for aromatic/polydiene groups. U.S. Pat. No. 6,841,626 also discloses a hydrogenated polymer with a saturation degree of polystyrene group in 98.4%.
However, currently the partial saturation technology provides polymers with saturation degrees of aromatic groups either too high or too low. The saturation degree higher than 90% is unflavored due to the loss of chain flexibility. The saturation degree lower than 20% is also undesired due to the insufficient stability. Therefore, there is a need to provide a new partially hydrogenated polymer with an appropriate saturation degree to fit the application requirements.